1. Field of the Invention
The present invention generally relates to an air intake apparatus serving as a passage for supplying air to an engine, and also relates to a manufacturing method therefor. More particularly, the invention relates to an air intake apparatus in which noise generated at the time of air intake is reduced, and to a manufacturing method therefor.
2. Description of the Related Art
In an air intake system of an engine, air taken in from an introduction port of an engine body is supplied to an engine body through an air intake passage portion connected from this introduction port to the engine body. This intake passage portion is provided with an air intake duct communicating with the introduction port. Generally, this intake passage portion is also provided with various intake members, such as an air cleaner, a throttle body, and an intake manifold, together with the intake duct. These intake members constitute a part of the intake passage portion.
Incidentally, in this intake apparatus, noise is generated in the intake passage portion during air intake. This noise leaks out of the intake apparatus from the introduction port, and propagates to the inside or outside of a passenger compartment. Therefore, hitherto, various means for reducing this intake noise have been developed.
A technique of providing an opening in a part of the intake passage portion and covering this opening with a porous member is known as means for reducing intake noise (see, for example, Unexamined Japanese Patent Publication No. 2001-193587). As described in this publication, noise can be reduced by forming an opening in a part of the intake passage hole and integrally covering this opening with a porous member. A reason therefor is considered as a synergistic effect of the following actions.    (1) Damping action due to elasticity of the porous member. Generation of acoustic waves due to vibrations of the intake passage portion is restrained.    (2) Action of viscosity and thermal conductivity of fine pores, which weakens energy of acoustic waves that get in fine pores of the porous member. The fine pores themselves resonate with variation in acoustic pressure, so that acoustic energy is attenuated.    (3) Action of a certain degree of air permeability that at least a part of the intake passage portion has. A part of acoustic waves passes through the part of the intake passage portion, so that the generation of standing waves is restrained.
Incidentally, according to a method of manufacturing an air intake apparatus as described in the aforementioned JP 2001-193587, the opening is covered with the porous member by heating and welding a peripheral portion of the opening and then pushing the porous member against the heated and molten portion. In this case, molten resin permeates into fine pores of the porous member. Then, the molten resin is solidified in the fine pores. Thus, the solidified resin serves as an anchor. Consequently, welding between the porous member and the intake passage portion can favorably be performed.
Meanwhile, it is necessary for reliably reducing intake noise to cover the opening with the porous member without leaving spaces therein. That is, in the case where an outer edge of the opening is not reliably sealed with the porous member, and where a part directly communicating with the outside of the intake passage portion is provided in the opening, pressure leaks from this unsealed part. Therefore, intake noise is not reduced. On the contrary, noise due to vibrations of the porous member itself sometimes occurs.
It is necessary for reliably sealing the outer edge of the opening with the porous member to dispose the porous member at a place corresponding to the opening when pushing the porous member against the opening. However, for instance, when the opening is provided in a curved surface of the intake passage portion, the opening has a curved shape. Thus, it is sometimes difficult to securely place the porous member against the opening. Therefore, in such a case, it is necessary that the porous member is disposed at a place corresponding to the opening, and that the placement position of the porous member with respect to the opening is regulated in some way.
The aforementioned JP 2001-193587 discloses a related method of pushing the porous member while the porous member is held by a porous-member receiving jig, which is separately prepared, so as to regulate a position, at which the porous member is disposed, with respect to the opening. However, there is necessity for forming such a porous-member receiving jig in such a way as to have a shape suited to that of the intake passage portion, in which the opening is formed, so as to place the porous member along the outer edge of the opening that has a three-dimensional shape. Therefore, this related method has problems in that a same porous-member receiving jig cannot be adapted to variously shaped intake apparatuses, and that the manufacturing cost of the apparatus thereof increases. Alternatively, according to another related method of covering the opening with the porous member by pushing the porous member against a preliminarily molten peripheral portion of the opening, the peripheral portion and the porous member once pushed thereagainst are instantaneously welded together. Thus, this related method has a problem in that because the placement position of the porous member cannot be corrected even when that of the porous member with respect to the opening is displaced, a manufacturing loss occurs, and that the manufacturing cost of the apparatus increases.